I’m no expert, but when using the Blues 6/8 songs, I think the BPM’s are wrong. If, for example, Blues 3 - 6/8 says it’s at 84 BPM, I would say it’s either at 168 BPM (8th notes), or 42 BPM (half notes). But saying it’s 84 based off of quarter notes is not right… that’s not how you feel 6/8 time. That’s 3/4 time, based off of quarter notes.
Mathematically equal, but musically they couldn’t be MORE different. Try this: download a BPM app on your phone, and try to tap along with any of those 6/8 beats. You will ALWAYS get the BPM’s to be twice as much or half as much as the BeatBuddy says.